Tuned GS1000. Should I weld the crank?

[Anonymous]

My tuned GS1000 engine recently spun its crank while on the dyno.
The bike produces about 110BHP at the wheel, and has 36mm flatslides, stage 1 cams, 1085 Wiseco kit, gasflowed head and some other stuff.
On the last run the #1 crankpin turned causing the piston to contact the valves.

My question is: Should I get the crank welded when I rebuild the engine, or was this an unlucky one-off? I have other standard cranks to fit if needs be.
The crank that twisted had been rebuilt once before, just a strip, clean, index and press together, but I had been told that it is safe to do GS1000 cranks twice before the fits become too loose.
Most people I have spoken to think that I shouldn't have needed a welded crank on a mildly tuned bike like this. What do you guys think?

Thanks in anticipation.

 

[Paul]

While you've got the crank out of the motor I would get it welded.
It doesn't cost a lot, and whilst you're mates are probably right that a "mildly tuned bike" doesn't really need a welded crank, it can't do any harm to weld it.
Anyway 2 ways to look at it
- if it had been welded before, it wouldn't have spun this time
- your "mildly tuned bike" needs a welded crank

 

[Paul]

One thing that I forgot to mention, if you do get it welded make sure that you really clean it well before you install it - welding slag/spatter is as hard as glass & you don't want that inside your motor!

 

[Anonymous]

Thanks Paul.

Am I right in thinking that you have had some experience with souped-up GS thou's?

 

[cbxchris]

WELD IT!!! I spun a stock crank on a stock 1000 in 78. They will rebalance also if sent to someone like falicon. It does need to be tig welded.

 

[saaz]

If it has spun once, best to get it welded while apart..can't hurt! And costs nothing much while apart.

I remember from an article I have on the original Wes Cooley superbike that they had cranks specially pressed together with special loctiite type stuff (like the gear loctite) whick solved any reliability problem. The factory welded some crank journals in later ngines, so there must be a reason to do it when the power goes up. Cheaper than valves etc.

 

[Anonymous]

Thanks for the responses.

My crank will be getting welded next week.

Funny though, when I asked certain "experts" about this before I tuned the engine, the reply was that GS1000 cranks "shouldn't need to be welded except for turbo/nitrous/stage 3 tunes".

Beware of the "should" word!!

 

[Paul]

Yes, you could say that!
I used to drag a GS thou - held the number 2 plate in The ACU national championships, that was against all the fuel bikes, I was only running petrol + a whiff of nitrous! To be fair, I did so well because of reliability of my GS as opposed to nitro burning kwackers.
By the way, when I was building my GS motor I went to see a very well known GS tuning expert in Manchester. He actually told me not to bother with shim under buckets, but to use standard buckets and make my own shims! Thinking about it he also said that it was a waste of time welding the crank because it put it out of balance!

 

[Anonymous]

Definately weld it!! I race a GS 1000. Currently 138hp at the rear wheel. While you are getting it welded, try to get it disassembled and the bearings checked. When new, these cranks are pretty much indestructable. When used (or abused) the big end bearings are subject to sludge build up and small rust spots on the pin. Here is NZ we have had 4 cranks let go the big end bearing (always #3 for some reason) and crunch the engine. My own blow up cost me all my pistons and valves, bent cam, camchain, cases, oil pump, crank etc etc. At least my head was fixable!!

Good luck.

Craig
Auckland, NZ

 

[Anonymous]

By the way, when I was building my GS motor I went to see a very well known GS tuning expert in Manchester. He actually told me not to bother with shim under buckets, but to use standard buckets and make my own shims! Thinking about it he also said that it was a waste of time welding the crank because it put it out of balance!

Hmmm, that could only be one person!

Craig, thanks for the info. Your blow up sounds a lot pricier than mine. My crank is with some good engineers (Paul, you may know SEP) who will check out every bearing before welding.

 

[Anonymous]

fwiw if you can, ask them to weld it with 312 stainless it doesn`t have a high ultimate tensile strength but it does have a high delta ferrite content that makes it highly resistant to cracking. also is it a chrome molly (4140) material or cast iron = high carbon content and requires a preheat that keeps the weld from cooling to fast setting up the carbon in a state that is very brittle not to mention in the heat effected zone at least 350 deg F pre heat and the same for a light post heat to help eliminate stresses set up during the welding .make sure it is tig welded by an experienced hand and not be an experiment on someones learning curve .just my humble opinion .Mark

 

[Paul]

I had a crank (for my old GT500!) done by SEP years ago - not cheap, but good.
I never bothered with balancing the GS cranks after welding, they are so good to begin with. I used to have a lot of work done with NCK Racing (gone now) They started to send cranks for balancing to Wilkinson Dynamic Balancing. Trevor Wilkinson checked a couple, then sent them all back saying that they were already balanced! And Trevor is good.

 

[Anonymous]

Thanks for the replies folks.

 

[Anonymous]

can someone help me out here, what exactly do you weld on the crank?

i am a welder myself and i cant see why/what you would weld to the crank?

 

[cbxchris]

If you will look at the crank pins you can see where they are pressed through to the counter weights...there is where the welding takes place...also on the main drive gear and several tack the bearing races. Under severe load they will slip causing a out of balance crank plus it puts the rods at a uneven throw. I`ve spun two in my time...one was even welded. They need to be tig welded.